MAGNETIC DISTURBANCES. 137 



simultaneity of many magnetic storms, which are transmit- 

 ted for thousands of miles, and indeed almost round the en- 

 tire circumference of the earth, as on the 25th of September, 

 1841, when they were simultaneously manifested in Canada, 

 Bohemia, the Cape of Good Hope, Van Diemen's Land, and 

 Macao ; and I have also given examples of those cases in 

 which the perturbations were of a more local kind, passing 

 from Sicily to Upsala, but not from Upsala farther north in 

 the direction of Alten and Lapland. In the simultaneous 

 observations of declination which were instituted by Arago 

 and myself in 1829 at Berlin, Paris, Freiberg, St. Petersburg, 

 Casan, and Nikolajew, with the same G-ambey's instruments, 

 individual perturbations of a marked character were not 

 transmitted from Berlin as far as Paris, and not on any one 

 occasion to the mine at Freiberg, where Reich was making 

 a series of subterranean observations on the magnet. Great 

 variations and disturbances of the needle simultaneously with 

 the occurrence of the Aurora Borealis at Toronto certainly 

 occasioned magnetic storms in Kerguelen's Land, but not at 

 Hobarton. When we consider the capacity for penetrating 

 through all intervening bodies, which distinguishes the mag- 

 netic force, as well as the* force of gravity inherent in all 

 matter, it is certainly very difficult to form a clear concep- 

 tion of the obstacles which may prevent its transmission 

 through the interior of the earth. These obstacles are anal- 

 ogous to those which we observe in sound-waves, or in the 

 waves of commotion in earthquakes, in which certain spots 

 which are situated near one another never experience the 

 shocks simultaneously.* Is it possible that certain magnet- 

 ic intersecting lines may by their intervention oppose all fur- 

 ther transmission ? 



We have here described the regular and the apparently ir- 

 regular motions presented by horizontally-suspended needles. 

 If by an examination of the normal-recurring motion of the 

 needle we have been enabled, from the mean numbers of the 

 extremes of the horary variations, to ascertain the direction 



Sabine, Unusual Disturb., vol. i., pt. i., p. xiv.-xviii. ; where tables are 

 given of the simultaneous storms at Toronto, Prague, and Van Die- 

 men's Land. On those days in which the magnetic storms were the 

 most marked in Canada (as, for instance, on the 22d of March, the 

 10th of May, the 6th of August, and the 25th of September, 1841), 

 the same phenomena were observed in the southern hemisphere m 

 Australia, See also Edward Belcher, in the Phil. Transact, for 1813, 

 p. 133. 



* Cosmos, vol. i., p. 212. 



